Microwave amplifier



Jan. l0, 1956 J. R. PIERCE 2,730,647

MICROWAVE AMPLIFIER Filed June 22, 1949 2 Sheets-Sheet 1 TE RMI NA T/ONi e a a i nl s /A/VENTOR By J. R. P/ERCE A T TORNE V Jan. 10, 1956 J. R.PIERCE MICROWAVE AMPLIFIER 2 Sheets-Sheet 2 Filed June 22, 1949/NVENTOVR 5V J. R. P/ERCE 771962,17 ATTORNEY United States Patent OMICROWAVE AMPLIFIER John R. Pierce, Millburn, N. J., assigner to BellTelephone Laboratories, Incorporated, New York, N. Y., a corporation ofNew York n ApplicatonJune 22, 14949, Serial No. 100,718 16 Claims. (ci.315-3) This invention relates to high, frequency amplifying devicesWhich utilize electromechanical interaction between two groups ofcharged particles to secure gain. Amplifiers of this general type aredisclosed in the 'application of W. B. Hebenstreit and I. R. Pierce,Serial No. 38,928, tiled July i5, 1948.

One object of the invention is to increase the gain of a double-streamamplifier by intermingling the two groups of charged particles ascompletely as possible.

Another object is to increase gain by increasing the density of thecharged particles in the interacting region.

A further object is to produce as great a charged particle density aspossible without drawing a large amount of' current from a supplysource. n A still further object of the invention is to enable adouble-stream amplifier to amplify in either direction.

In previous double-stream amplifiers, a pair of closely coupled streamsof charged particles (e. g., electrons) are projected along apredetermined path in the same direction at respective differentvelocities. Atthe beginning of the path at least one stream is modulatedunder the control of a signal which is to be amplied. As pointed out inthe above-noted Hebenstreit-Pierce application,

Y electro-mechanical interaction between the charged particles of therespective streams causes the impressed variations to grow in amplitudeand amplied signal energy is withdrawn at the end ot the path. Gain isdependent to a large degree upon the closeness of the coupling betweenthe two streams, being maximum when the charged particles of the twostreams are completely in teriningled.

In accordance with the present invention, a stream of charged particlesfrom one source is projected in a predetermined direction to interactwith charged particles from another source traveling in a differentdirection. Disturbances impressed upon the stream of charged particlesemanating from the rst source are amplified by energy interchangesbetween the charged particles from the respective sources whiley suchparticles are traveling in different directions. It has been found thatit is possible' to achieve greater intermingling of the chargedparticles of different groups with less difficulty when the particlesare traveling in different directions than when they travel in the samedirection. Gain is, therefore, correspondingly enhanced. Certainembodiments of the invention have the additional advantage of enabling agreater density of charged particles to exist in the interacting regionthan would be practical in a conventional double-stream arnplier withoutdrawing increased current from a supply source. Other embodiments havethe additional advantage of allowing the direction of amplification tobe re- I I be attained from a study of the following detaileddescription of several specific embodiments and an inspection of theaccompanying drawings, in which:

Fig. l illustrates an amplifier utilizing the interaction between a pairof oppositely directed electron streams to secure gain;

Fig. 2 shows an amplifier which makes use of a group of electrons movingsubstantially at right angles to a signal-bearing electron stream tosecure gain; and

Fig. 3 represents alternative means for causing electrons to movesubstantially at right angles to the signalbearing stream and may beapplied to the amplifier of Fig. 2 along the lines X-X.

Referring particularly to Fig. 1, the embodiment of the invention shownmakes use of two oppositely directed electron streams.. Most of thestructure is enclosed by an elongated cylindrical glass vacuum envelope10. Envelope 10 is enlarged somewhat at either end to accommodateelectron emissive structures. f

Within the enlarged portion at the left-hand end of envelope 10 is athermionic cathode 11. Cathode 11 is a short metal cylinder and isaxially aligned with envelope 10. Its left-hand portion is hollow andcontains a heating coil 12 which is connected by a pair of leads 13 and14 across a battery 15. Leads 13 and 14 pass through the left-hand endof envelope 10 and hold coiled heater 12 in place. Cathode 11 is held inplace by a pair of leads 16 and 17 which are attached at diametrcallyopposite points on its outer surface and extend through the left-handend of glass envelope 10. Lead 17 is connected to a movable tap on amain supply battery 18. The right-hand face of cathode 11 has a raisedannular emitting portion 19 which is coated with electron-emissivematerial to emit a tubular beam of electrons when heated.

At the opposite end of envelope 10, within the enlarged portion, is asimilar cathode 20 with an annular coated raised emitting portion 21facing to the left. Cathode 20 contains a heating coil 22 which isconnected by a pair of leads 23 and 24 to a battery 25. Heater 22 issupported within cathode 20 by leads 23 and 24, which pass through theright-hand end of envelope 10. Cathode 20 is supported by a pair ofleads 26 and 27 which also pass through the right-hand end of glassenvelope 10 and which are attached to diametrically opposite points onthe outside surface of cathode 20. Lead 27 is connected to a movable tapon supply battery 18.

A short tubular metal electrode 28 is axially aligned with and supportedby glass envelope 10 and is located just to the right of cathode 11. Ashort wire helix 29 is located to ythe right of electrode 28 and is alsosupported by glass envelope 10. Helix 29 is connected to electrode 28 bya short straight conductor 30 and its righthand end is terminated in itscharacteristic impedance by power dissipative or lossy material 31 (e.g., a thin coating of colloidal graphite) on the outside surface ofenvelope 10. Lossy material 31 begins at the righthand end of helix 29and extends to the left for approximately a quarter of its length. Thelossy coating 31 may be made lighter toward its left-hand end in orderto give a gradual terminating effect and prevent reflections. A lead 32is attached to electrode 28, passes through the left-hand end ofenvelope 10, and is connected to the most positive terminal of battery18.

An input wave guide 33 is coupled to helix 29 by straight conductor 30.Envelope 10 passes through wave guide 33 substantially normal to itsbroad surfaces, with the inside surface of the left-hand wall of waveguide 33 ush with the right-hand end of electrode 28. Straight couplingconductor 30'extends for about half the width of guide 33. One end ofwave guide 33 is closed and the other may be connected to an inputsignal source.

The right-hand end of envelope 10 contains elements substantiallysimilar to those included at the above-described left-hand end. A shorttubular electrode 34, corresponding to electrode 28, is located just tothe left of cathode 20 and a short wire helix 35, corresponding to helix29, is situated to the left of electrode 28. Both electrode 3ft andhelix 35 are supported by glass envelope 1? and they are connected by ashort straight section 35. Helix 35 is terminated in its characteristicimpedance at its left-hand end by lossy material 37 on the outsidesurface of envelope 10. The distribution of lossy material 37 is similarand complementary to that of lossy material 31 at the left-hand end ofhelix 29. A lead 38 is attached to electrode 34 and is connected, afterpassing through the right-hand end of envelope 1G, to the most positivepole of battery 18.

An output wave guide 39 corresponds to input wave guide 33 and iscoupled to helix 35 by straight section 36. Envelope passes through waveguide 39 substantially normal to its broad surfaces. The inside surfaceof the right-hand wall o guide 39 is flush with the left-hand end ofelectrode 34. One end of wave guide 39 is closed and the other may becoupledy to a load.

An elongated tubular metal electrode 40 occupies mest of the spacebetween the right-hand end of helix 29 and the left-hand end of helix35. Electrode 40 is at least several wavelengths long at signal.frequencies and has an outside diameter substantially equal to theinside diameter of envelope 10. it serves to shield the main electroninteraction region of the amplifier from external effects and todetermine the potential of that region. Electrode 40 is supported byglass envelope 10 and is spaced slightly from helices 29 and 35. At anintermediate point, electrode 40 is attached to a lead 4I which passesthrough the wall of glass envelope 10 and is connected to a movable tapon battery 18.

Electrode 40 is made positive with respect to cathodes 11 and 20 byappropriate settings of the variable taps on battery 18 and cathode 11is made negative with respect to cathode 20. When cathode 11 is heated,raised portion 19 emits a tubular stream of electrons which areaccelerated to the right by electrode 28. The electrons travel to theright within envelope 10 and are eventually collected by cathode 20. Thestream is f0- cused by an additional annular raised portion 42 whichsurrounds raised portion 19 on they right-hand side of cathode 11 and bythe longitudinal magnetic field established by a solenoid 43 whichsurrounds and is concentric with envelope 10.y Solenoid 43 is suppliedwith directcurrent from an appropriate source (not shown).

When cathode 20 is heated, raised portion 21 emits a tubular stream tothe left. The electrons are accelerated by electrode 34, pass throughhelix 35 and; electrode 40, and are largely collected by helix 29 andelectrode` 28. The stream is focused by the eld set up. by solenoid 43and. by an additional annular raised. portion 44 which surrounds raisedportion 21 on the left-hand end. of cathode 20.

When an input signal is applied to wave guide 33, it is transferred tohelix 29, which serves to couple the signal to theelectron stream. Helix29 is Wound. with a pitch such that the wave which travels along ittravels at approximately the same velocity as the electrons emitted fromcathode 11. The stream traveling to the right is density-modulated byinteraction. with the field established by the signal as it istransmitted along helix 29. The electrons traveling to the left interactelectromechanically with those traveling to the right, causing thevariations impressed upon the stream of the latter electrons to grow in.amplitude. The streamv of electrons traveling to the right may thus besaid to support a space charge wave of negative attenuation.

As explainedin the above-identiiied copending Hebenstreit-Pierceapplication, double-stream gain of this type is characterized byelectromechanical rather than electromagnetic coupling between the twostreams of electrons. Electromechanical coupling involves direct inter'-action between the streams themselves rather than. by way ofelectromagnetic fields in or around a nearby conductor or resonator. Atypical. characteristic of electromagnetic coupling by way of aconductor or resonator is that approximately the same amount of storedmagnetic energy as stored electric energy is involved. In directelectromechanical coupling between two groups of electrons, on the otherhand, the magnetic stored energy is much less than the stored electricenergy and plays no important role in electromechanical interaction.

The pitch of helix 35 is substantially the same as that of helix 29,enabling the amplified variations to be transferred to helix 35. As theamplified signal energy reaches the right-hand end of helix 35 andstraight portion 36, it is transferred to wave guide 39 and is availablefor application to an appropriate load.

Since the two electron streams are oppositely directed, they are easierto intermingle than they would be if they were like directed. When twolike-directed streams are intermingled, they are projected fromdifferent cathodes andv mechanical difficulties make completeintermingling diicult to obtain. The two cathodes emitting like-directedstreams are usually placed in a side-by-side, a concentric, or a tandemrelationship. In the first two, intermingling is partial even at best;in the last, one stream may be projected through apertures in the othercathode, but the intermingling is still far from complete. ln Fig. l,the streams are oppositely directed, and cathodes 11 and 2Q are locatedat opposite ends of the electron path, where they do not interfere withelectron intermingling. Coupling between streams is greatest when thetwo streams of a double-stream amplifier are completely intermingled.Therefore, since the oppositely directed streams may be more completelyintermingled than like-directed streams, coupling, and hence gain, iscorrespondingly increased.

In general, amplification will take place when the oppositely directedstreams travel at different velocities and/or have different chargedensities. Gain may be adjusted and optimized at any particularfrequency of operation by adjusting the variable taps on battery 18. Forcertain frequency ranges, if the charge densities are equal, optimumgain will occur when the faster stream is traveling to the right; forothers, when the faster stream is traveling to the left. The electronsfrom cathode 29 can be made faster or slower than those from cathode 11by making cathode 20 negative or positive, respectively, with respect tocathode 11. If it is desired to vary the respective stream chargedensities in addition to or instead of the stream velocities, the heatervoltages supplied by batteries 15 and 25 may be adjusted.

The tube shown in Fig. l has the additional advantage of being able toamplify in either direction. For example, if the relative potentials ofcathode 1 and cathode 20 are reversed by appropriate adjustment of thevariable taps on battery 18, the tube will amplify from right to leftrather than from left to right. Wa\.'c guide 39 will. become the inputguide and wave guide 33 the output guide. The reversing may beaccomplished, for example, by means of a relay 44 and a switch 45. Whenswitch 45 is open, relay 44 is not actuated and cathodes 11 and 20 areconnected as previously described. When switch 45 is closed, relay 44 isactuated and the respective connections from cathodes 11 and 2t) tosupply source 18 are reversed.

Fig. 2 shows a modification of the double-stream arnplifier of Fig. l inwhich electrons are projected in an interacting relationship with, butsubstantially at right angles to, the electron stream bearing the inputsignal. As in Fig. l', most of the structure is enclosed by an elongatedcylindrical glass vacuum envelope 10, the lefthand end of which isenlarged to accommodate :in electron-emissive structure.

The cathode structure at the left-hand end of envelope 10 issubstantially the same as described in connection with Fig. l, and aninput wave guide 33 is similarly coupled to an input helix 29. There isno cathode, however, at the right-hand end of envelope 10. Rather, theelectrons emanating, from cathode 11 are collected by' a avancee ycatedat the left-hand end of envelope 10, is connected to the negativeterminal of source 18.

A short tubular metal electrode 48 is located to the left of collector46 and is supported by envelope 10. Electrode 48 is attached to a lead49 which passes through the right-hand end of envelope and is connectedto the positive pole of direct-current source 18. A short wire outputhelix 37, corresponding to helix 37 in Fig. 1, is situated Vto the leftof electrode 48 and is connected to electrode 48 by a short straightconductor 36. The lefthand end of helix 37 is terminated by a thin layerof lossy material 31 distributed on the outer surface of envelope 10.

Envelope 10 passes through an output wave guide 39 with its axissubstantially normal to the broad faces of the guide 39, whichcorresponds to output wave guide 39 inFig. 1. Straight conductor 36couples output helix 35 to wave guide 39. As an alternative to thearrangement of electrode 3.4 in Fig. 1, the inside surface of therighthand Wall of output wave guide 39 is flush with the righthand endof electrode 48, and the right-hand end of helix 35 extends lto theleft-hand wall of wave guide 39. Straight conductor 36 is connected toelectrode 48 approximately half way between the broad faces of .waveguide 39.

As in Fig. 1, a solenoid 73 surrounds and is concentric' with envelope10 and is supplied with current from an appropriate direct-currentsource (not shown). Solenoid 43, when energized, sets up a longitudinalmagnetic focusing iield within envelope 10. Also as in Fig. 1, a tubularmetal electrode 40 is located in the space between helices 27 and 3S andis supported by glass envelope 10. The length of electrode 40 ispreferably at least several wavelengths in the electron stream emanatingfrom cathode 11. Greater lengths give greater available gain.

When cathode 11 is heated, a tubular stream of electrons is projected tothe right, lengthwise of and within envelope 1i). The emitted electronsare collected by the collector' electrode 46. A signal supplied to inputwave guide 33 is transferred to the stream in the manner described inconnection with Fig. 1.

The element which produces the second electron stream is a tubularthermionic cathode 50. Cathode 50 is concentrically mounted withinenvelope 10 and electrode 40 and its outside diameter is slightly lessthan the inside diameter of the Istream of electrons emitted by cathode11. Cathode 50 extends for most of the length of electrode 40 and has anelectron-emissive coating on its outer surface.

Cathode 50 is heated by an internal heating coil S1 which is connectedto cathode Si) at its left-hand end. A ceramic bushing S2 is located atthe right-hand end of cathode 50. The right-hand end of heating coil 51is connected to a lead 53 which passes through bushing 52. Lead 53 istaken out through the wall of glass envelope 10 and an opening inelectrode 40 and is connected to one side of a heater supply battery 54.Lead 53 also serves to support the right-hand end of cathode 50. Thelefthand end of cathode 50 is supported by a lead 55 which passesthrough the wall of glass envelope 10 and an opening in electrode 40 andwhich is connected to the other side of heater supply battery 54.

Tubular electrode 4i) is held positve with respect to cathode Si) by abattery 56 and serves as an anode. Lead 41, which is attached toelectrode 40 and taken out through the wall of glass envelope 10, isconnected to the positive pole of battery 56 and the negative pole ofbattery 56 is connected to lead 55. Finally, lead 55 is connected to avariable intermediate tap on direct-current source 18. f

Cathode 50 is heated by heating coil 51 and emits electrons radiallyoutward towards tubular anode electrode 40, with no axial velocitycomponent. The electrons from cathode 50 may either reach electrode 40or be turned back by the magnetic field produced by solenoid 43,depending on the strength of this ield relative to the voltage ofbattery 56. In either case, the cloud of electrons from cathode 50interacts with the electron stream from cathode 11 to produce gain atfavorable frequencies. The mechanism of interaction is much the same asin any double stream amplifier in which the longitudinal velocity of onestream of electrons is allowed to approach zero, but with theconstruction of Fig. 2 a large charge density of electrons with zerolongitudinal velocity can be produced. Gain may be optimized at adesired frequency by adjusting the voltage of direct-current source 56,the magnetic field, and the tap on source 13 which controls thepotential of cathode 50 with respect to cathode 11.

The electrons projected from cathode 50 travel substantially at rightangles to the direction of travel of the electrons emanating fromcathode 11. Cathodes 11 and 50 do not interfere with one another,enabling the electron intermingling to be more complete than ispractical when two like directed streams are employed. Available gainis, therefore, increased by a corresponding amount.

The voltage of battery 56 may be adjusted relative to the strength ofthe magnetic focusing field to minimize the electron current iiowbetween cathode 50 and the surrounding tubular anode electrode 40. Ahigh electron density in the interacting region is thereby achievedwithout necessitating a large power drain on battery 56. Available gainis correspondingly high.

The central cathode 50 and associated positive electrode 40 shown inFig. 2 may be rearranged as shown in Fig. 3. Here the cathode is a metaltube 61 which is concentrically mounted Within envelope 10. The insidediameter of cathode 61 is slightly larger than the outside diameter ofthe electron stream. The inside surface of tubular cathode 61 is coatedwith electron-emissive material. A heating element 62 is coiled aroundthe outside of cathode 61 and the assembly is supported from glassenvelope 10 by three or more spaced ceramic rods 63. The opposite endsof heating coil 62 are brought out through the wall of glass envelope 10and connected across the heater supply battery 54. Heating coil 62 iselectrically connected to cathode 61 at its left-hand end and iselectrically insulated from cathode 61 over the rest of its length by acoating of insulating material on the outside surface of the latter.

An anode 64 comprises a wire extending lengthwise of and concentric withcathode 61. The opposite ends of anode 64 are brought out through thewall of glass envelope 10 for supporting purposes. Anode 64 is heldpositive with respect to cathode 61 by battery S6, the voltage of whichmay be adjusted to give optimum gain. Battery 56 is connected betweenthe left-hand ends of heating coil 62 and anode 64 and the negative sideof battery 56 is connected to a variable tap on direct-current source 18of Fig. 2.

The operation of cathode 61 and anode 64 is substantially the same asthat of cathode 50 and electrode 40. described in connection with Fig.2, except that the electrons move radially inward from cathode 61 towardanode 64. As does the arrangement of Fig. 2, this structure gives highelectron density in the interacting region along with relativelycomplete intermingling with the signal-bearing stream. Gain, therefore,is high. In addition, the power drawn from battery 56 is small if thevoltage of battery 56 is adjusted to give a small net current flowbetween cathode 61 and anode 64. The variable tap on battery 18 and themagnetic focusing field may be adjusted for optimum operation.

It is to be understood that the above-described arrangements areillustrative of the application of the principles anadur of theinvention. Numerous other arrangements may be devised by those skilledin the art without departing from the spirit and scope of the invention.

What is claimed is:

l. A high frequency amplifier comprising a first source of chargedparticles positioned to direct a stream of charged particles along apredetermined path and a sccond source of charged particles positionedalong said path to direct charged particles substantially at rightangles to said stream along a substantial portion of said path, thecoupling between the charged particles from said first source and thecharged particles from said second source along the gain-producingportion of the length of said stream consisting substantially only ofelectromechanical coupling, whereby a signal supported by said stream isamplified by cumulative interaction along said portion of said pathbetween the charged particles from said rst Source and the chargedparticles fro n said second source.

2. A high frequency amplifier in accordance with claim 1 in which saidstream is tubular and said second source is cylindrical and concentricwith said stream to project charged particles radially in substantiallyall directions perpendicular to the axis of said stream.

3. A high frequency amplifier in accordance with claim l in which saidstream is tubular and said second source is positioned within saidstream to project charged particles radially outward in substantiallyall directions perpendicular to the axis of said stream.

4. A high frequency amplifier in accordance with claim l in which saidstream is tubular and said second source is cylindrical, concentric withsaid stream, and located outside of said stream to project chargedparticles radially inward in substantially all directions perpendicularto the axis of said' stream.

5. An amplifying space discharge device which comprises an enclosuredefining a path of travel for charged particles, a first chargedparticle source positioned at one end oi said path to direct a tubularstream of charged particles along said path, a charged particlecollector positioned at the other end of said path, means responsive toan input signal to modulate said stream, a cylindrical second chargedparticle source positioned coaxially with said stream at an intermediatepoint along said path to project charged particles radially insubstantially all directions perpendicular to the axis of said stream,the charged particles from said second source being substantiallycommingled with the charged particles from said tirst source comprisingsaid stream and the coupling between the charged particles from said`first source comprising said stream and the charged particles from saidsecond source along the gain-producing portion of the length of saidstream consisting substantially only oi electromechanical coupling,whereby the variations impressed upon said stream are increased inamplitude as the charged particles comprising said stream pass thosefrom said second source, and means responsive to variations in saidstream for withdrawing amplified signal energy.

6. A space discharge device comprising an enclosure which defines a pathof travel for charged particles, iirst source ot' charged particlespositioned at one end of said pat. to direct a stream of chargedparticles along said path and a second source of charged particlespositioned at an intermediate point along said path to produce chargedparticles in the space through which said stream travels, the chargedparticles from said second source having a velocity component lengthwisealong said path of substantially zero, the lengthy orn the region alongsaid path in which the charged: particles from said second source existbeing at least several wavelengths in said stream, and the coupling`between the charged particles of said stream andthe charged particlesproduced by said second source along the gain-producing portion of thelength or said stream consisting, substantially only' ofelectromechanical coupling, whereby cumulative interaction between thecharged particles of said stream and the charged particles produced bysaid second source amplities a signal appearing in said stream.

7. An amplifying space discharge device which comprises means providinga signal wave transmission path, means to convey signal wave energyalong said path in a predetermined direction, a source of chargedparticles, and means to direct charged particles from said source acrosssaid path over a major portion ot its length in a continuous andcumulative interacting relationship with the conveyed signal wave and ina direction substantially at right angles to said predetermineddirection, whereby said signal wave energy is caused to increase as itprogresses along said path.

S. An amplifying space discharge device which conipriscs means providinga path of travel for charged particles, a first source of chargedparticles positioned at one end of said path to direct a stream ofcharged particles along the length of said path, means surrounding atleast a portion of said path to coniine moving charged particles to saidpath, means at one end ot path to modulate said stream under the controlof signal wave energy, :a second source of charged particles positionedalong said path to supply a cloud oi charged particles at anintermediate portion ot said path over a distance of at least severalsignal wavelengths in said stream, the charged particles comprising saidcloud having a velocity component lengthwise along said path ot'substantially zero and the coupling between the charged particlescomprising said stream and the charged particles comprising said cloudalong the gain-producing portion of the length or said stream consistingsubstantially only electromechanical coupling, whereby cumulativeinteraction between charged particles in said cloud and those in saidstream produces gain, and means at the other end of said path towithdraw amplified signal wave energy from said stream.

9. An amplifying space discharge device in accordance with claim 8 inwhich said means to modulate said stream includes aperiodic couplingmeans.

l0. An amplifying space discharge device in accordance with claim 8 inwhich said means to withdraw ampliiied signal wave energy from saidstream includes aperiodic coupling means.

l1. An amplifying space discharge device which comprises an electron gunand a first collector electrode spaced apart to deiine a path of travelt'or electrons, means coupled to said electron gun to direct a streamot` electrons from said gun to said first collector. an elongatedelcctron emissive electrode extending lengthwise along said path for adistance of at least several signal wavelengths in said. stream, asecond coflcctor electrode situated substantially coaxially with saidelongated cle-:- tron emissive electrode and extending oversubstantially the same portion of said path, means coupled to saidelongated electron emissive electrode to direct electrons radially ofsaid stream in substantially all directions perpendicular to the axisthereof from said elongated clectron emissive electrode to said secondcollector, moans coupled to said stream between said gun and saidclongated electron emissive electrode to supply signal wave energythereto, and means coupled to said stream between said elongatedelectron emissive electrode and said first collector to Withdrawamplified signal wave cn therefrom.

l2. An amplifying space discharge device in accordancer with claim llin' which said elongated electron emissive electrode is locatedcentrally within said st eam and said second collector is tubular and islocated outside of said stream surrounding said elongated electronemissive electrode.

13. An amplifying space discharge device in accordance with claim l1 inwhich said second collector is located centrally within said stream andsaid elongated Por electron emissive electrode is located outside ofsaid streamsurrounding said collector.

' Y path within said envelope for a distance of at least several signalwavelengths in said stream between said accelerating electrode and saidrst collector, a second collector electrode situated substantiallycoaxially with said second cathode within said envelope and extendingover substantially the saine portion of said path, means conpled to saidsecond cathode to direct electrons radially of said stream insubstantially all directions perpendiculzn to the axis thereof from saidsecond cathode to said second collector, means coupled to said streambetween said accelerating electrode and said second cathode to supplyrsignal wave energy thereto, and means coupled to said stream betweensaid second cathode and said first collector to withdraw amplied signalwave energy therefrom.

15. An amplifying space discharge device in accordance with claim 14 inwhich said second cathode is located centrally within said stream andsaid second co1- lector is tubular and is located outside of said streamsurrounding said second cathode.

16. An amplifying space discharge device in accordance with claim 14 inwhich said second collector is located centrally within said stream andsaid second cathode is located outside of said stream surrounding saidsecond collector.

lcerences Cited in the le of this patent UNITED STATES PATENTS 2,317,140Gibson Apr. 20, 1943 2,320,860 Fremlin June l, 1943 2,338,237 FremlinIan. 4, 1944 2,406,370 Hansen et al. Aug. 27, 1946 2,457,989 De ForestJan. 4, 1949 2,479,084 Rosenthal Aug. 16, 1949 2,578,434 Lindenblad Dec.11, 1951 2,652,513 Hollenberg Sept. 15, 1953 2,684,453 Hansell July 20,1954 OTHER REFERENCES Article by A. V. Hollenberg, pp. 52-58, incl.,Bell System Tech. Journal, January 1949.

Article by A. V. Haetf, pp. 4-10, incl., Proc. I. R. E., January 1949.

